It has been conventionally required that coatings for light-sensitive materials be uniformly applied using coating liquid compositions to cover a support to form photographic layers such as photographic emulsion layers used in the production of photographic materials. In JP-A-52-115214 (corresponding to U.S. Pat. No. 4,001,024: the term "JP-A" as used herein means an "unexamined published Japanese patent application"), an attempt is made to form uniform coated layers by coating the lowermost layer with a low-viscosity coating composition having a viscosity of about 1 to 8 cp to form a thin lowermost layer and coating a layer just above the lowermost layer with a relatively high-viscosity coating composition having a viscosity of about 10 to 100 cp. In this method, the surface of a web is wetted by using the low-viscosity coating composition to form the lowermost layer so as to prevent a coating failure, or to act to improve the lower-coating liquid composition has good adhesion with upper layer.
JP-A-63-11934 discloses a method for preparing silver halide photographic materials wherein at least the lowermost layer is coated with a hydrophilic colloid solution containing a high-molecular weight compound having a sulfo group, a sulfuric ester group or a carboxyl group on its side chains and having a limiting viscosity number ([.eta.], dl/g, measured in 0.1N of NaCl aqueous solution at 30.degree. C.) of 0.4 to 1.8, at a rate of 80 to 300 m/min, when silver halide emulsions or other hydrophilic colloid layers are coated. This patent application discloses the production of photographic materials (including films), for example, by using a coating liquid composition whose viscosity is adjusted to 50 to 80 cp by adding poly(sodium p-styrenesulfonate) having [.eta.]=1.0. This application also disclose a method wherein unevenness in coating is reduced.
With regard to multi-layer co-coating methods, a method using a multi-layer slide hopper is disclosed, for example, in JP-B-33-8977 (corresponding to U.S. Pat. No. 2,761,791: the term "JP-B" as used herein means an "examined Japanese patent publication"). This specification discloses that there is no limitation with regard to the number of layers to be co-coated with different coating liquid compositions which can be co-coated on a support by using a multiple slide hopper of this type.
However, such a method suffers the problems of non-uniform surfaces, due to unevenness in co-coating, which is expected to occur as fine irregularities on a support, as the number of layers in the coating is increased. There has been great difficulty in stably obtaining a uniform co-coated surface which is free from color non-uniformity, particularly at a high coating speed. Accordingly, layers have been conventionally coated by using two or more sets of coating procedures, when color photographic materials having many layers, particularly 8 or more layers are to be prepared.
The above process is illustrated in greater detail as follows. When 8 or more total layers of coating are provided by conventional multi-layer co-coating, non-uniformity in color density (that is, lack of color uniformity) is expected to occur due to various problems, e.g., bubbling on the slide surfaces of syringes, flow caused by irregularities on the surface of a support, a flow caused by setting air at the early stage of drying stage, and similar types of problems. These problems are liable to be remarkable by fluctuation of the coating amount when the concentration of each coating liquid composition is increased.
Accordingly, when 8 or more total photographic layers are to be co-coated, it is necessary that turbulence at the interface of the slide surface of the syringe is reduced, coating liquid compositions are co-coated on a support conveyed at a high speed without being affected by irregularities on the surface of the support and the co-coated surface is kept uniform at the drying stage.